1. Field of the Invention
The present invention relates to a local area communication network for data communication, having application to, for example, computer-to-computer data traffic, terminal-to-terminal data traffic, and the like.
2. Discussion of Background
A great deal of discussion can be seen in the recent literature regarding local networks and their applicability to many of today's local area communication needs. In recent times, the need to develop computer networks capable of data communication between one computer and another computer used by Local Area Communication Networks has increased, and in particular, there is a real need for a system for exchanging a large amount of information such as image data efficiently, free of error, and rapidly.
The existing Local Area Communication Network (hereinafter referred to as LAN) is commonly a packet switched network in which the data transmitted from a data sending node is temporarily stored in a packet switching exchange connected to a data sender where the data is divided into a plurality of units each of which is called a packet and the data in turn is transferred, for each packet unit, to a data receiving mode. There the packets are reassembled into the original data format.
Typically, data is placed on a commony shared communication bus to which each node, which is usually a computer station, is coupled. The conventional data sending and receiving system is next briefly described.
When a sending station receives a call originating signal transmitted from a sending terminal, the call originating signal is detected by a transmission control and, in response to the detection, a send data counter and a packet assembly counter are reset. At this time, a link establishing signal sender permits a link establishing signal to be transmitted to a receiving station. Upon receiving the link establishing signal, the receiving station permits a call signal sender to apply a call signal to a receiving terminal. Then, when the receiving station receives an answer signal at the receiving terminal, the communication link between the sending and receiving terminals is ready for establishing a communication link. Under this condition, a received packet counter and a data assembly counter are reset for receiving a packet from the sending station, and a link establishing ready signal is issued to the sending station. Upon receiving the link establishing ready signal, the sending station drives a communication ready signal sender to transmit a communication ready signal to the sending terminal thereby resulting in establishing the communication link between the sending terminal and the receiving terminal. After establishing of such communication link, data transmitted from the transmitting terminal is divided into packets whichin turn are delivered via available routes selected at that time by a host computer, for example, which provides overall control of communication among the nodes of the network. Each packet is routed through a switching office to the receiving station. The receiving mode reassembles the received packets into the original format of the data intended to be sent to the receiving mode. On the other hand, the receiving terminal issues a correct checking answer indicating the received data is correct or an incorrect checking answer indicating that the received data is erroneous. The receiving station receives these checking answers and modifies the packets to the correct packet form.
In this manner, each node in the local area communication network systems has been burdened with the tasks of establishing the communication link, addressing, common bus management, and generating a handshake over the bus back to the sender, etc.
To do these tasks, most networks have the appropriate protocols, which are used to perform each task efficiently in each layer of the layered network, which is organized as a series of layers designated for different functions.
In conventional data transmission systems, data, address and control information are transmitted through the commonly shared bus, and time to process addresses, as well as control information within the protocol in the corresponding layer, is required. This greatly increased the overhead so that the time required to transfer data increases.